Viscose process



May 17, 1960 N. L. cox

VISCOSE PROCESS Filed Aug. 2, 1955 If'ig. 1

VISCOSE COAGULATING BATH CONTAINING FORNALDEHYDE AND FREE I 0F HEAVYMETAL SALTS OPTIONAL STRETCHING STRETOHING IN A REGENERATING v BATHAFTER TREATNENT TOTAL STRETCH AT LEAST 300 In INVENTOR NORMAN LOUIS COXBY 7M ATTORNEY VISCOSE PROCESS Norman Louis Cox, Wilmington, Del.,assignor to E. L du Pont de Nemours and Company, Wilmington, Del., acorporation of Delaware Application August 2, 1955, Serial No. 526,064

Claims. (Cl. 18-54) 1 the spin bath. As disclosed in the above patent,the gel filaments can be stretched up to a limit of 140% in a secondarybath with a corresponding increase in tenacity to slightly over 4grams/denier. As shown in the examples of the patent, the process wasapplied specifically to filaments of 2.5 denier/filament (100 denier/40filaments).

An object of the present invention is to provide further improvements instretchability, tenacity, dry and wet' modulus. Another object is toprovide a process particu-' larly applicable to fine denier yarns, i.e.,yarns composed of filaments up to 1.5 denier/filament. Such yarns areuseful for preparing sheer textile fabrics, as reinforcement forthermosetting resins, etc. Other objects will appear hereinafter.

The objects are accomplished by a processwhich comprises extruding ahighly xanthated (at least 23% xanthate sulfur based on cellulosecontent) viscose spinning solution through a plurality of orifices intoan aqueous coagulating but non-regenerating bath free of heavy metalsalts and containing by weight about 0.2% to 1.0% (preferably 0.3% to0.8%) formaldehyde, from 2% to 11% (preferably 3% to 6%) sulfuric acidand 0 to 12% (pref erably 8% to 12%) sodium sulfate, the sum of sulfuricacid and sodium sulfate concentrations being from 8% to 16%, to formfilaments, and stretchingthe coagulated The measurements areconventional with the possible 2,937,070 Patented May 17, 1960 notcontain any heavy metal salts such as zinc sulfate; and that the stretchis applied after the filaments leave the coagulating bath in at leastone regenerating bath or partly in air and partly in at least oneregenerating bath.

By adhering to the process steps set forth above, stretches of 300% to450% (amounts unheard of in prior processes) can be applied. Theresulting filaments display smooth surfaces substantially free ofcrenulations or indentations and uniform, undifferentiated, circular orslightly elliptical cross-sections. The'yarns are extremely strong,displaying tenacities of 5.5 grams/denier to as high as 8 grams/denier.Optimum results are obtained in the production of yarns havingfilamentdeniers less than 1.5, particularly 0.3 to 0.6 denier/filament. At thesedeniers, elongation and other important physical properties of the yarnsare maintained at the most satisfactory level. Figure 1 is a schematicdiagram of the process of the present invention.

The invention will be more clearly understood by referring to theexamples and discussion which follow. Unless otherwise stated, allpercentages in the specification and claims are by weight. Example 3sets forth the best mode contemplated for carrying out the'invention.The other examples set forth specific embodiments of the processinvented. The examples are not to be construed in any sense aslimitative of the invention.

In the tables the following symbols are used:

Ta are tenacities in grams/denier; dry, wet and loop EdWYl arepercentelongations; dry, wet and loop G.S. isthe gel swelling factorexception of the gel swelling measurement. Gel swelling was determinedaccording to the following procedure. The yarn,'composed of thecoagulated filaments, was col- I lected on a feed wheel or Godet-wheelover a period of two minutes after leaving the coagulating bath. The

' sample was then Wrapped in cheese cloth; centrifuged filaments to themaximum extent (300% to 450%) while passing them through at least oneaqueous regenerating bath (preferably containing 1% to 4% sulfuricacid);

In a specific embodiment, there is. added to the 'viscose solution priorto extrusion 0.5% to 2% based on the weight of viscose of analkali-soluble coagulation modifier selected from the group consistingof ethers of j the formula RO-(CH CH O),,--R', whereR is alkyl or aryl,n is an integer from 1 to 4 and R ishydrogen, alkyl or aryl andpolyethylene oxides of molecular weight between 200 and 2,000. By theterm alkali-soluble coagulation modifier is meant a modifier that issoluble in 6% aqueous sodium hydroxide to the extent of at least 1%.

It should be emphasized that no substantial stretch occurs in thecoagulating bath; that the coagulating bath has substantially noregenerating action, i.e., that it decomposes less than 30% of thexanthate groups originally present in the viscose by the time the gelfilament enters the secondary bath; that the coagulating bath must (3600rpm.) for two minutes in a basket centrifuge; and weighed in a closedbottle. The sample was then treated with acid to regenerate cellulose;washed free of acid; dried in an oven at C.; and weighed again. Theratio of the first weight (the gel weight) to the second weight (thecellulose weight) is the gel swelling.

Xanthate sulfur content, another term used in the examples and which isa measure of the degree of xan-' A 10 gram sample thation, wasdetermined as follows. of viscose wasdissolved in water and neutralizedto a pH of 6.8 by the addition of sodium phosphate. Nitrogen was thenbubbled through the viscose solution to drive off hydrogen sulfide andcarbon disulfide resulting;

from'the decomposition of sodiumtrithiocarbonate and other by-products.The resulting solution of cellulose xanthate was then acidified with 5to 10 cc. of phos phoric acid; boiled for /2 hour while bubblingnitrogen through-the solution to' drive off carbon disulfide resultingfrom the decomposition of cellulose xanthate. The

carbon disulfide was collected in a methanol-potassium EXAMPLE I Aviscosesolution containing 5% cellulose having a degree ofpolymerization (D.P.) of 525, 6% sodium hydroxide, and 1% oftetraethylene glycoldimethyl ether was prepared in the following manner;Alkali cellulose was first prepared from cotton linters and aged to getthe desired viscose viscosity (30 to 60 poises). Then, the alkalicellulose was xanthated for 4.5 hours at 25 C.

a aaao'zo using 62% carbon disulfide, based on the weight of bone- 9 drycellulose. The resulting xanthate crumbs were dissolved in aqueoussodium hydroxide. After mixing for 1.5 hours at a temperature below 15C., tetraethylene glycol dimethyl ether was added and mixing wascontinued for 10 minutes. The freshly prepared viscose was filtered coldand kept at C. until it was spun.

The viscose solution was spun in a relatively unripened state, with ahigh xanthate sulfur content (39.5% xanthate sulfur based on cellulosein the viscose) and with a low sodium trithiocarbonate content. It wasspun into 270 denier, 240 filament yarn, i.e., a filament denier of1.12, by extrusion through a spinneret having orifices of 0.0025"diameter into a primary coagulating bath at 50 C. The primary bathcontained sulfuric acid, 0.8% formaldehyde and no sodium sulfate. Theyarn was given a primary bath travel of approximately 30 inches by usinga roller guide. No substantial tension was imposed on the yarn since thefeed wheel speed did not exceed the jetvelocity. After leaving thecoagulating bath where no stretch occurred, the yarn was given 133%stretch in air and then stretched in a bath.

containing 1% sulfuric acid at 95C. to a total of 3 90%. The yarn wascollected at a windup speed of 28 yards/minute. The spinning apparatusand collection device were essentially the same as those usedcommercially in the so-called bobbin or spool process. The resultingyarn was then washed, finished, dried without stretch and twisted threeturns per inch in the conventional manner.

The properties of the yarn prepared as described above (yarn A) arelisted in Table I below, together with those of a yarn (yarn B) spunfrom the same viscose in the same manner but with a primary bathcontaining,

' in addition to 10% sulfuric acid and 0.8% formaldehyde, 26% sodiumsulfate, i.e., a regenerating bath.

It will seen that, with the use of the dilute, nonregenerating primarybath, it is possible to apply twice the amount of stretch possible witha concentrated, re-

viscoses containing 4% cellulose (DR 600) and 5.5%

, ample II, but at different filament deniers (by using spinnerets withdifferent numbers of orifices). The temperature of the primary bath was25 C.

The yarns were stretched varying amounts in a secondary hath at 95 C.containing 2% sulfuric acid and 20% sodium sulfate and then in atertiary bath of 1% sulfuric acid at 95 C. The yarns, designated as A,B, C, and D in Table II below, were collected on a bobbin as in ExampleI except for yarn B which was collected in a relaxed state by allowingit to fall on a tray. All yarns were processed as in Example I.

Table II shows, for each case, the xanthate sulfur content of theviscose, the gel swelling factor of the yarns, the denier per filamentand the yarn properties. It will be seen that the dry tenacities were inthe extremely high range of 7.2 to 7.7 grams/denier.

Table II Yarn A Percent Xanthate. Percent Stretch-.. Denier/Filament..-

ewe-awn.-

l ws-wwwsodium hydroxide and no coagulation modifier was prepared using62% carbon disulfide. This viscose, which contained 37.7% Xanthatesulfur, was spun as in Example generating bath. The resulting yarn has adry tenacity 2.3 grams/denier higher than that of the control yarnEXAMPLE 'II' A viscose containing 4% cellulose (DP. 600), 5.5% sodiumhydroxide and no coagulation modifier was prepared according to theprocedure of Example I, using 50% carbon disulfide and a 3.5 hourXanthation time. This viscose, which contained 31.2% Xanthate sulfur,was spun as in Example 1 into a coagulating bath containing 3.7%sulfuric acid, 10% sodium sulfate and 0.5% 7

salt, and wound on a bobbin. The yarn was processed,

and tested as in'Example I, and found to have dry, wet and loop,tenacities of 7.5, 5.9, and 3.8 grams/,dfinier, respectively.

' EXAMPLE III Following the general procedure of Examplev I, two.

Iinto a primary bath at 50 C. containing 10% sulfuric acid, no sodiumsulfate and 0.8% formaldehyde. The,v gel yarn was stretched in asecondary bath and then in a tertiary bath, each bath containing 2%sulfuric acid and 20% sodium sulfate and maintained at C. Under theseconditions, it was possible to stretch the yarn 382%. Wh n 'c nt l yamwaspun rom h me s s under essentially the same, conditions, but withoutformal; dehyde in the primary bath, it was only possible to obtainstretch. Table III below shows the properties of these two yarns. Itwill be seen that, in the, presence of formaldehyde, considerably higherdry, wet and loop tenacities were obtained.

Table II Example IV EXAMPLE V A viscose containing 4% cellulose ('D.P.600), 5'i5'% sodium hydroxide and 1% polyethylene glycol (averagemolecular weight 1540) was prepared with 44% carbondisulfide. It wasspun in the urlripened state and at a xanthate sulfur content of 26.7%vinto'a primary bath containing 4% sulfuric acid, 1.0%.- sodium, sulfateand.

0.3% formaldehyde at 25 C. The yarn was stretched as a in Example II(two baths) to a total of 3l5%. The properties of this yarn and those ofa control yarn spun from the same viscose under the same conditions butin A viscose containing 5% cellulose (D.P. 525) and 6% sodium hydroxidewas prepared using 40% carbon disulfide according to the generalprocedure of Example I. It was spun in an unripened state and at axanthate sulfur content of 25.5% into a primary bath at 24 C. containingsulfuric acid, no sodium sulfate and 0.8% formaldehyde. The yarn wasstretched 430% while it was passed through two regenerating baths at 95C., each containing 2% sulfuric acid and 20% sodium sulfate. The yarnwas processed as in Example I. The properties of this yarn and those ofa control yarn spun from the same viscose under the same conditions, butin the absence of formaldehyde are shown in Table V below.

EXAMPLE VII A viscose containing 2% of cellulose (D.P. 900 to 1000) and4% sodium hydroxide was prepared by the general procedure of'Example Iusing 50% carbon di- This viscose having a xanthate sulfur content of29% was spun into a primary bath at 25 C. containing 4.6% sulfuric acid,10% sodium sulfate and 0.8% formaldehyde. The coagulated gel yarn wasstretched a total of 342% in a regenerating secondary bath at 95 C.containing 2% sulfuric acid and 20% sodium sulfate and in a tertiarybath at 95 C. containing 1% sulfuric acid. The yarn, which had a gelswelling factor of 5.4 and a filament denier of 0.6, was processed as inExample I. It displayed the following tenacities: 7.4 dry, 5.8 wet and3.9 loop; and the following elongations: 5.0% dry, 5.5%

wet and 2.6% loop.

In the process of this invention, a variety of viscoses may be used.They may be prepared from cotton linters or wood pulp or fromothercellulose sources or mixtures. The degree of polymerization (D.P.) ofthe cellulose does not have nearly as great an influence on the level ofyarn tenacity as do other variables such as primary bath concentrationand composition. However, although the normal cellulose of the industry(D.P. 300 to400) are suitable, best results (high tenacity combined withgood elongation) are obtained with cellulose of D.P. 500 to 1000.

The composition of the viscose may also vary. Cellulose'contents from 2%to' 8% or more and allgali contents from 4% to 8% or more aresatisfactory. Prefered are the dilute viscose solutions, i.e., thosecontaining from 2% to 5% cellulose and from 4% to 6% alkali. In anycase, the concentration of the viscose solution must be adjusted inrelation to the D.P. of the cellulose to provide a viscose viscosity of30 to 100 poises.

The alkali cellulose may be completely xanthated in the xanthating churnor xanthated partially in the churn and partially in the mixer.Splitting xanthation so that not over is completed in the churn isdescribed in a copending U.S.'patent application, Serial No. 351,592,filed April 28, 1953, now Patent No. 2,801,998, to A. Robertson. Ineither type of xanthation, conventional or split, it is imperative thatthe ultimate xanthate sulfur content of the viscose, based on cellulose,be at least 23%, preferably from 25% to 35%. These relatively highxanthate sulfur contents are obtained by using a total of at least 35%,preferably about 40% to about 50% carbon disulfide (based on cellulose).v

The viscose, after being filtered and deaerated, is preferably spun inan unripened condition, i.e., at a salt index exceeding 7 and usuallymuch higher. It is one of the advantages of this invention thatunripened viscose solutions can be used, thereby saving ripening timeand equipment. However, viscose prepared with large amounts of carbondisulfide, e.g., 55% to 65%, are advantageously slightly ripened tobring the xanthate sulfur content within the optimum range.

As illustrated in the examples, coagulation modifiers which areeffective in baths free of heavy metal salts such as zinc salts can beadded to the viscose. include the previously described ethers andpolyethylene oxides. The ethers include such compounds asphenoxyethanol, ethoxyethanol, methoxyethoxyethanol,butoxyethoxyethanol, phenoxyethoxyethanol, ethoxyethoxyethoxyethanol,butoxyethoxyethoxyethanol, phenoxyethoxyethoxyethanol,butoxyethoxyethoxyethoxyethanol, phenoxyethoxyethoxyethoxyethanol,l-ethenyloxy-Z-methoxyethylene, ethylene glycol diethyl ether,triethylene glycol diethyl ether, tetramethylene glycol diethyl ether,triethylene glycol dimethyl ether, diethylene glycol diethyl ether, etc.The polyethylene oxides are those of the formula RO(CH CH O),,H, where nis at least equal to 4, i.e., polymers which have a molecular weight ofat least about 200, and which in addition have the necessary solubilityin viscose. Those polyethylene oxides having molecular weights betweenabout 300 and about 2000 are preferred. It should be understood that itis possible, and sometimes desirable, to use mixtures of two or more ofthe above-described coagulation modifiers. In any case,

the total concentration in the viscose should be between about 0.5% and2%. Optimum results are obtained with concentrations between 0.75% and1.5%. The used these specific coagulation modifiers leads to yarnshaving somewhat increased tenacities and elongations as compared withyarns prepared in the absence of modifiers.

The viscose spinning solution is then extruded into the primary bath.The viscose may be at the normal ambient temperature, 18' C. to 25 C.,or it may be heated to 40 C. to 50 C. or higher prior to spinning. Theprimary bath is desirably at a temperature not exceeding 50 C. Thepreferred primary bath temperature is 25- 50 C., and the normal ambienttemperature, e.g., 1825 C., can be used. The primary bath is an aqueousacidic coagulating bath, having generally a pH between 1 and 2. It isnon-regenerating because of the presence of formaldehyde. It is believedthat formaldehyde stabilizes the xanthate groups by forming cellulosehydroxymethyl xanthate. This compoundis relatively stable even at lowpH, but its formation in substantial amounts requires rapid mary bath ata sufiiciently low level. In aflirming this.

theory, I have found that the sum of the concentrations These modifiers(based on the weight of the primary bath) of sulfuric acid and sodiumsulfate should be in the range of 8% to 16%. Of these two ingredients,sulfuric acid should always be present in amounts between about 2% andabout 11%. With less than this amount, the primary bathdoes not have asufliciently rapid coagulating action. With more than this amount theregenerating effect (decomposition of the xanthate groups) becomes toogreat to permit the desired high stretching in a subsequent step. Asshown in the examples, I have also found that it is permissible todispense with sodium sulfate altogether. Furthermore, I believe thatsalts of heavy metals, i.e., of metals of specific gravity above 4 suchas zinc sulfate, iron sulfate or chromium sulfate, retard thepenetration of formal dehyde. Therefore, the presence of these saltsshould be avoided. By adhering to the above limitations on theprimarybath above 70%, and generally nearly 100% of the xanthate groupsoriginally present in the viscose remain undecomposed at the time thegel filament enters the secondary (regenerating) bath. This compares tothe primary baths of the prior art wherein, not more than 20% to 35% ofthe original xanthate groups are still intact when the filament enters asecondary bath.

The best results are obtained Where the primary bath contains bothsulfuric acid and sodium sulfate, the first one in the range of 3 to 6%and the second one in the range of 8 to 12% provided always the sum ofthese concentrations is in the range of 8 to 16%..

Another effect of the low total acid-salt concentration and the absenceof heavy metal salts in the primary bath is to form coagulated filamentshaving relatively high gelswelling factors. This permits the use of alarger number of spinneret holes to produce finer filaments than can beproduced with conventional, more concentrated spinning baths. Ingeneral, the gel-swelling factor of the yarns obtainable by this processlies between 3.5 and 6.2, high enough to permit spinning of fine denierfilaments and still low enough to provide optimum yarn properties. Thisis contrary to the teachings of recent art on high tenacity yarnmanufacture (see U.S. Patent 2,535,044) where very low gel-swellingfactors (within the range of 2.5 to 3) were preferred.

The relatively highly swollen state of the filaments of this inventionalso seems to permit rapid penetration of formaldehyde to effectstabilization of the xanthate groups. Therefore, small amounts offormaldehyde (0.2% to 1.0% and preferably between 0.3% to 0.8%) can beused successfully. In fact, the use of more than about 1% offormaldehyde in the coagulating bath is undesirable since the yarn thenbecomes too highly plasticized and less tension can be applied to it,The optimum amount of formaldehyde varies with the spinning speed, morebeing desirable at the higher speeds. The formaldehyde should contactthe yarn before any appreciable stretch is applied to the yarn. However,the formaldehyde should not be applied to the yarn before coagulationhas begun. Thus, if theformaldehyde is mixed with the viscose prior toextrusion, it has been found that the stretchability of the yarn is notincreased and the desired results are not achieved.

After leaving the primary bath, the filaments are passed through atleast one secondary bath (hot dip bath or stretching bath) which has aregenerating action on the cellulose xanthate, i.e., decomposes theXanthate groups. The secondary bath may consist simply of aqueoussulfuric acid in concentrations of about 1% to 4%, or it may alsocontain a dehydrating salt, preferably sodium sulfate, in concentrationsof 2% to 25%. The presence the stretch should be applied in thesecondary bath or.

baths between positively driven rollers traveling at different speeds.Normally, the yarn travels about to 30 inches in the primary bath andabout to 30 inches in of salt in the secondary bath tends to preventoverplasticization and sticking of filaments. The secondary bath shouldbe free from formaldehyde except for the very small amounts which may becarried from the primary bath. It should also be free of added heavymetal salts. if desired, a second regenerating bath or tertiary bath mayhe used. This bath is also an aqueous sulfuric the secondary bathsystem. Stretch is applied in the secondary bath or baths to the extentof at least300% and up to 450% or more, of the 'unstretched length ofthe yarn. Such extraordinarily high stretches are possible because theyare applied to the coagulated, but substan-' tially non-regenerated yarnas described. The desirable operating tension on the yarn is between 60%and of the breaking tension.

The bobbin process has been used in most of the examples but it isimmaterial whether spinning is done -'by the bobbin, bucket orcontinuous processes. It is possible to realize some increase inelongation without undesirable sacrifice of tenacity by collecting theyarn'in the relaxed state on a tray or platform.

Following spinning, the yarn is washed free of acid and salt and thendried under tension, according to conventional procedures. If preferred,the yarn may be twisteror slasher-dried to enable the dry elongation ofthe finished product to be controlled.

Spinning may also be carried out with the aid of spinning tubes such asdescribed .in Millhiser U.S. Patent 2,440,057 or in Drisch et al. U.S.Patent 2,511,699. These tubes of relatively small diameter and ofsubstantial length confine the filaments in their critical stage offormation. By maintaining the speed of the cocurrent bath-flow throughthe tube only slightly below the speed of the filament bundle passingthrough the tube, no substantial tension is imposed on the filaments. Itis thus possible to increase materially the rate of spinning withoutsubstantial sacrifice in yarn properties. Spinning speeds can varyfromthe 25 to 30 yards per minute used in small scale, experimentalequipment to yards per minute or more used in industrial processes.

This invention makes it possible to prepare low filament denier yarnswith strengths considerably higher than considered possible heretofore.The. yarns are produced using less chemicals in the bath than previouslyused and at practical spinning speeds.

The improved yarns obtainable through the process of this invention canbe used instead of regular regenerated cellulose yarns for any purposewhere thelatter find application. The yarns'are particularly desirablefor use in sheer wearing apparel where superior strength is desired; inindustrial applications such as filter cloths, strainers, etc.; in thepreparation of non-woven fabrics by forming mats imbedded inthermo-setting resins; in laminates having layers of fabric betweenlayers of plastics; and in the bulk polymerization of Vinyl monomers toproduce fiber-reinforced moldings,

As many widely dilferent embodiments may be made without departing fromthe spirit and scope of the invention, it is understood that theinvention is not limited except as defined in the appended claims.

The invention claimed is:

l. A process for the production of high tenacity regenerated cellulosefilaments which comprises extruding a xanthated viscose spinningsolution, the xanthated viscose containing at least 23% xanthate sulfurbased on the cellulose content, through a plurality of orifices into anaqueous coagulating bath free of heavy metal salts dehyde, from 2% to11% sulfuric acid and up to 12% sodium sulfate, the sum of sulfuric acidand sodium.

2. A process as in claim 1 wherein the coagulated filaments arestretched 300% to 450% while passing through at least one aqueousregenerating bath containing 1% to 4% sulfuric acid to form filaments ofup to 1.5 denier/filament.

3. A process as in claim 1 wherein the viscose,spinning solutioncontains from 2% to 8% cellulose, from 4% to 8% alkali and has axanthate sulfur content of at least 23% based on the weight of cellulosein the viscose solution.

4. A process as in claim 1 wherein the viscose solution contains 0.5% to2% of an alkali-soluble coagulation modifier selected from the groupconsisting of (A) ethers of the formula RO-(CH CH O),,R', where R isselected from the group consisting of alkyl and aryl, n is an originallypresent in the viscose, and stretching the cov agulated filaments atleast 300% while passing them through at least one aqueous regeneratingbath containing a major percentage of water and a minor percentage ofsulfuric acid.

7. A process as in claim 6 wherein the coagulated filaments arestretched, 300% to 450% while passing through at least one aqueousregenerating bath containing 1% to 4% sulfuric acid to form filaments ofup to 1.5 denier/filament. v

8. A process as in claim 6 wherein the viscose spinning solutioncontains from 2% to 8% cellulose, from 4% to 8% alkali and has axanthate sulfuric content of at least 23% based on the weight ofcellulose in the viscose solution.

9. A process'as in claim 6 wherein the viscose solution contains 0.5% to2% of an alkali-soluble coagulation modifier selected from the groupconsisting of (A) ethers integer from 1 to 4 and R is selected from thegroup consisting of hydrogen, alkyl and aryl and (B) polyethylene oxidesof molecular weight between 200 and 2000.

5. A process is in claim 1 wherein the viscose solution contains 0.75%to 1.5% of an alkali-soluble coagulation modifier selected from thegroup consisting of (A) ethers of the formula RO(CH CH O),,-R', where Ris selected from the group consisting of alkyl and aryl, n is an integerfrom 1 to 4 and R is selected from the group consisting of hydrogen,alkyl and aryl and (B) polyethylene oxides of molecular weight between200 and 2000. l

6. A process for the production of high tenacity regenerated cellulosefilaments which comprises extruding a xanthated viscose spinningsolution, the xanthated viscose containing at least 23% xanthate sulfurbased on the cellulose content, through a plurality of orifices into an:aqueous coagulating bath free of heavy metal salts and containing byweight about 0.3% to 0.8% f0rma1- dehyde, from 3% to 6% sulfuric acidand 8% to 12% sodium sulfate, the sum of sulfuric acid and sodiumsulfate concentrations being from 8% to 16%, to form of the formulaRO(CH CH O),,-R', where R is selected from the group consisting of alkyland aryl, n is an integer from 1 to 4 and R is selected from the groupconsisting of hydrogen, alkyl and aryl and (B) polyethylene oxides ofmolecular weight between 200 and 2000.

10. A process as in claim 6 wherein the viscose solution contains 0.75to 1.5 of an alkali-soluble coagulation modifier selected from the groupconsisting of (A) ethers of the formula RO(CH CH O),',,R, where R isselected from the group consisting of alkyl and aryl, n is anintegerfrom 1 to 4 and R is selected from the group consisting of hydrogen,alkyl and aryl and (B) polyethylene oxides of molecular weight between200 and 2000.

References Cited in the file of this patent UNITED STATES PATENTS GreatBritain Nov. 10, 1943

1. A PROCESS FOR THE PRODUCTION OF HIGH TENACITY REGENERATED CELLULOSEFILAMENTS WHICH COMPRISES EXTRUDING A XANTHATED VISCOSE SPINNINGSOLUTION, THE XANTHATED VISCOSE CONTAINING AT LEAST 23% XANTHATE SULFURBASED ON THE CELLULOSE CONTENT, THROUGH A PLURALITY OF ORIFICES INTO ANAQUEOUS COAGULATING BATH FREE OF HEAVY METALY SALTS AND CONTAINING BYWEIGHT ABOUT 0.2% TO 1.0% FORMALDEHYDE, FROM 2% TO 11% SULFURIC ACID ANDUP TO 12% SODIUM SULFATE, THE SUM OF SULFURIC ACID AND SODIUM SULFATECONCENTRATIONS BEING FROM 8% TO 16%, TO FORM FILAMENTS CONTAINING ATLEAST 70% OF THE XANTHATE GROUPS ORIGINALLY PRESENT IN THE VISCOSE, ANDSTRETCHING THE COAGULATED FILAMENTS AT LEAST 300% WHILE PASSING THEMTHROUGH AT LEAST ONE AQUEOUS REGENERATING BATH CONTAINING A MAJORPERCENTAGE OF WATER AND A MINOR PERCENTAGE OF SULFURIC ACID.